It is generally known that the most common reason for failure of rotary electric machines, far more than locked bearings, is burnout of field windings. Primary overheating is the main reason for motor and generator repair. For this reason fan cooled, externally ventilated, and totally enclosed motors and generators have been developed.
Recently in order to solve the burnout problem, emphasis has been on molding methods, and on molds for completely encapsulating the stator core and coils, or field windings. In U.S. Pat. No. 4,950,438, for instance, a four piece mold is employed to overcome the drip method, that is the method wherein the stator is drip coated on only one side at a time during a coating cycle, followed by then turning the stator to coat it on the other side. In U.S. Pat. No. 4,950,438 the stator is entirely in the upright position while being coated. The four mold members are combined with the stator so that a cavity is formed between them and the stator. Vehicle is then poured into that cavity through sprues until it flows out of drain holes in the lower mold member.
Another sprue-type method for tradting rotary electric machines is described in U.S. Pat. No. 4,362,490. It was believed that when the stator was entirely coated with vehicle too large a volume of vehicle was utilized at a cost which was too high. The invention, then, was to eliminate the coating on the periphery of the stator. To do so upper and lower mold members were utilized to define an inner space around the coil. Through a sprue leading to this space a material was injected so that it flowed into that space to permeate the coil.
Because of the large volume of vehicle required by other electromagnetic coil coating methods the drip method still appears to be popular as illustrated in U.S. Pat. No. 5,474,799. The vehicle baking or curing temperatures were a matter of concern in that instance. The problem was solved by keeping the temperature of the iron stator core below the vehicle curing temperature by utilizing several curing temperature stages.
A submersible can-type electric motor, stated to be well-known, is the subject of U.S. Pat. No. 4,496,866. The bore of the stator core has a cylindrical can inserted therein to cover its inner wall. A vehicle is then inserted to be molded completely about the external surface of the stator core including the end portions of the coils.
In addition to vehicle-molded rotary electric machines such as those described, two related patents, U.S. Pat. No. 3,874,073 and U.S. Pat. No. 3,758,799, disclose the use of sand and other particulate materials such as alumina, mica, chalk, zirconia, beryllium oxide, and naturally occurring minerals, as heat dissipating matter around the windings which are supported on the stator core. Using a housing means around at least part of the stator the particulate material, along with vehicle, is forced in against the winding support.
It will be understood that one of the problems in utilizing sprues--or sprays as in FIG. 9 of U.S. Pat. No. 3,874,073--is that it is difficult, even when pressure is employed, to fill all of the interstices and to eliminate air voids in the stator windings. When the area formed by a mold is filled from above with a vehicle as viscous as those normally employed, it is difficult if not impossible to avoid the formation of air voids, pockets or pores. This is particularly true when particulate materials are incorporated in the vehicle. Voids are also difficult to prevent when the port holes used to enable air to escape from the windings are in the base of the mold. The prior art, then, is subject to certain disadvantages. By the practice of this invention a method and means are provided which overcome such disadvantages.